The present invention relates to a damper disc assembly used in an automotive clutch disc or the like, and more particularly to a damper disc assembly having a wide displacement angle range.
Typically, a damper disc assembly used in an automotive clutch disc is provided with an output hub having a flange formed integrally on its outer circumference, and a coil spring for circumferentially coupling an input plate and an input flange with each other. Furthermore, a separate hub type damper disc assembly has been proposed in which a flange is separated from the hub and a low rigidity spring member is provided for coupling both members with each other in the circumferential direction. In this type of damper disc assembly, a relative displacement angle between the input plate and the input hub is increased, and two-stage displacement characteristics of low rigidity and high rigidity may be obtained.
In the foregoing conventional separate hub type damper disc assembly, low rigidity spring members are provided in an inner circumferential portion of the flange. For this reason, the size of each low rigidity spring member is limited so that the degrees of freedom for designing is limited.
In general, in the damper disc assembly, in order to reduce undesirable sounds generated at a low cruising speed, it is necessary to suppress the displacement rigidity to a low level and to widen the displacement angle range. Accordingly, the conventional approach has been to provide the assembly with two torsion springs juxtaposed in series in the circumferential direction in a single window of the flange, and interpose a float member between the torsion springs. As a result, a displacement angle between the input plate and the flange is increased, so that the special sounds inherent in the low speed cruising may be reduced. Such a conventional damper disc assembly is disclosed in Japanese Utility Model Application Laid-Open No. Hei 1-141931. In this damper disc assembly, raised cut portions which are in contact with circumferential outer end portions of the torsion springs, are formed in a clutch plate and a retaining plate which belong to the input plate.
Also, there has been provided in a conventional damper disc assembly, a lubrication chamber, filled with lubricant fluid, formed between the clutch plate and the retaining plate for lubrication of contact parts between the two plates and the torsion springs. A drawn portion is formed between the clutch plate and the retaining plate to receive the torsion springs in this damper disc assembly.
In this damper disc assembly, a mechanical strength of the raised cut portions formed in the clutch plate and the retaining plate is lowered since a thickness of the plates is reduced by machining. Accordingly, damage is liable to occur in the raised cut portions.
Also, in the case where the drawn portions are formed in the clutch plate and tile retaining plate, a plurality of deeply drawn portions are required to be formed in the circumferential direction. Accordingly, it is difficult to perform the machining work and additionally, the mechanical strength is lowered.